Automatic inventory control systems often expedite the removal of items from an inventory. Libraries are one example of facilities in which automatic inventory control systems are used. Many libraries use an identification tag, such as a bar coded label, to identify some or all of their materials. By scanning the tag, the identity of the item can be retrieved from a database. When another tag on a patron's library card is scanned, the library item may be checked out to the patron.
Often, this check-out operation is performed by library personnel. However, many libraries are installing automated systems that allow patrons to check out books and other library materials by themselves. One example of an automated system begins with the patron presenting his library card to an automated check-out device which reads the identification tag on the card. Each item from the library is then sequentially placed on the device, the device reads the item's identification tag, and the item is recorded by the system as having been checked out to the patron.
There are also systems that prevent the unauthorized removal of items from the library. One example of such a system uses inventory control markers, such as magnetic strips, which can be activated and deactivated (e.g., demagnetized and remagnetized). An inventory control marker is provided in each book or other library item and a sensor is placed at the entrance and/or exit of the facility. To perform the inventory control function, each inventory control marker is activated prior to returning a library book or other item to the shelf. When the library item is checked out, the inventory control marker is deactivated. The patron may then walk past the sensor without actuating the alarm. However, if the patron attempts to walk past the sensor without checking the library item out, either purposefully or accidentally, then the alarm sounds and/or the patron is stopped by, for example, a gate. Presently, library personnel who check books out for patrons deactivate the inventory control marker manually.
Most conventional automated check-out devices also deactivate the inventory control marker in a library item which is checked-out. For a magnetic inventory control marker, this is typically accomplished by bringing a library item, having a magnetic strip (the inventory control marker) attached to it (typically near the spine of a book), near an electro magnet that generates a direct current (DC) field. However, if two or more books or other library items are placed on top of or next to each other in the automated check-out device, only one of the identification tags is read, but both inventory control markers may be deactivated. This would allow the patron to remove two or more library items while actually checking out only one. Thus, it is desirable to have a mechanism for determining whether there are multiple items on or in the check-out device.
One method currently used for determining the presence of two or more library items is to scan for the number of inventory control markers. For magnetic inventory control markers, this procedure typically includes using a constant magnetic field. This may be undesirable in certain situations, especially if other electronic devices are nearby, because interference may occur, resulting in improper functioning of these devices. Furthermore, there are often limits on the resolution of such systems which may make individual inventory control markers on items, such as thin books, cassette tapes, or CDs, difficult to individually resolve, so that the sensor may detect only a single marker. Furthermore, some library materials may not have inventory control markers. Thus, a need exists for a new and improved method of determining the number of inventory items in or on an inventory control device.